Black Oxide Test

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aliva

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I decide to do a test comparing 2 different black oxide treatments
I'll compare Brownells Oxpho-Blue to Caswell Plating's cold black oxide concentrate.
Product:
Brownells Oxpho-Blue 4 oz. U.S.
Cost from Amazon $34.54 $8.58/ U.S .oz. (taxes and shipping extra)

Caswell Plating Black Oxide concentrate 1 Pint imperial
Cost from Caswell $43.45 $ 2.17/ Imperial .oz taxes and shipping extra)

The Brownells solution was used as recommended undiluted from the bottle.
The Caswell was used directly from the bottle and undiluted, Caswell recommends dilution of 9 parts distilled water to 1 pint of concentrate.

The test pieces are 1/4" CRS freshly milled and cleaned with acetone, I divided the pieces in 1/2 with tape and numbered 1-4.
Pieces 1 and 2. The oxide solution was applied to each by rubbing in for 1 minute at an ambient temp of approx. 24C
Brownells on section 1
Caswell on section 2

Test pieces 3-4 was applied after the pieces were heated to approx. 100F
Brownells on section 3
Caswell on section 4

Conclusion:
Piece 1 Brownells at ambient temp show blackening but some color hues showing up not a solid black.
Piece 2 Caswell at ambient temp shows much better darkening and more uniform in colour.

Piece 3 Brownells at 100F shows better colour and even throughout.
Piece 4 Caswell at 100F shows similar to the Brownells in results.
NOTE. None of these pieces have been sealed with oil as per Caswells instructions, Brownells doesn't mention this in their instructions.

So Caswell shows a much better consistent result for 1/4 of the price.
Solutions.jpg
Ambient Temperature.jpg
Hot 100F.jpg
 
You know, cold rust blueing works pretty well and isn't very expensive. Hydrogen peroxide and common table salt. Steel will start to bubble and get rusty. This is good. After a while, just rinse off the rust and remove any loose stuff. Dunk the steel into boiling water. This converts the rust into magnetite, which is blue black. Boil for a couple of minutes. Repeat the peroxide/salt treatment and boiling, until the desired bluing is achieved. When I did some tee-nuts, it took about 8 cycles or so to look good. When the solution stops bubbling with the steel, either the solution is spent, or all of the steel has been converted to rust or magnetite.
PXL_20220219_215153345.jpg
 
I used several different gun blues. So so. I tried the method WobblyHand used. There is a video out showing step by step. It took multiple tries and doesn't look great. On the tee nuts they came out OK but the vise stop looked like a streaky blue-black. Tried different de-greasers and the only one guaranteed was brake cleaner. If you are experimenting, it is cheap and does work. oil well or wipe with grease to seal.
Currently using Caswell Mega Black. The finish is quick and looks like store bought. Will see how it lasts in use. Wanted something that after all day machining something looks like I bought it. You blacken at room temp for 5 minutes, rinse, soak in sealer for 2 minutes and let dry until next day.
 
Chewy said:
I used several different gun blues. So so. I tried the method WobblyHand used. There is a video out showing step by step. It took multiple tries and doesn't look great. On the tee nuts they came out OK but the vise stop looked like a streaky blue-black. Tried different de-greasers and the only one guaranteed was brake cleaner. If you are experimenting, it is cheap and does work. oil well or wipe with grease to seal.
Currently using Caswell Mega Black. The finish is quick and looks like store bought. Will see how it lasts in use. Wanted something that after all day machining something looks like I bought it. You blacken at room temp for 5 minutes, rinse, soak in sealer for 2 minutes and let dry until next day.
Click to expand...
As long as the solution is bubbling there's rust being made. Also one needs to card the rust so it is uniform. I used an old toothbrush. It's black now, no one will ever use it! Forgot to mention the carding, that's an important part of the process. It may have been beginners luck, but I think the tee nuts came out ok if you don't look too close. ;)

I used 12% peroxide.
 
Just looked, mine was only 3%. Biggest difference is the look. Tee nuts were fine. Vise stop wasn't. Also, I can be done one shot in less time then it takes to boil the water. The down side is the $80+ for the chemicals. Just made a 5C collet spanner wrench. Will see how it turns out with the Mega Black.
 
Chewy said:
Just looked, mine was only 3%. Biggest difference is the look. Tee nuts were fine. Vise stop wasn't. Also, I can be done one shot in less time then it takes to boil the water. The down side is the $80+ for the chemicals. Just made a 5C collet spanner wrench. Will see how it turns out with the Mega Black.
Click to expand...
Time & money, funny how that goes... I spent about $15 on the peroxide, still have lots left. Good luck with the mega black.
 
I e had good luck with G96brand and birch wood brand. The G96 is a pastey crystal solution. I like to hear the part alittle seems to absorb better into the metal. The birch wood is a liquid and also seems to get good results. When I get home I’ll post a pic I just did some tooling on Monday turned out good.
Why would caswell say no to oil after, that’s what gives the long term rust protection?
 
Cadillac said:
I e had good luck with G96brand and birch wood brand. The G96 is a pastey crystal solution. I like to hear the part alittle seems to absorb better into the metal. The birch wood is a liquid and also seems to get good results. When I get home I’ll post a pic I just did some tooling on Monday turned out good.
Why would caswell say no to oil after, that’s what gives the long term rust protection?
Click to expand...
Caswell does recommend a sealer Brownells does not
 
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Best blue/black is the US armory procedure, uses a 50/50 mixture of potassium nitrate and sodium nitrate melted in an iron or steel pot which is clean, not rusty, the mixture is raised to 900 deg.F and treated with manganese oxide to precipitate undesireable elements, the temperature lowered to 600-650 deg. F, the articles to be blued are immersed in the solution after being oiled, no prior cleaning being necessary, after a few minutes, the articles are removed and the color observed as to the color desired, from blue to black, if left in the bath too long, the color may degrade, after the color is reached, the articles are removed and quenched in cold clean water, then into boiling water to remove any salt adhereing on them, and finally into hot oil, time in the niter bath should not exceed 4 or 5 minutes, if longer than, the finish will be degraded to a dirty grey.
I have used this process, and it is quite durable, equal to factory gun finishes, the temperature used produces a spring temper, and the bath can be used for general tempering use at appropriate temperatures, once melted, the bath can be used at much lower temperatures for tempering use.
This information came from an American Machinist reference book sheet
 
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